The present invention relates to an apparatus for use in calibrating pressure transducers, such as those used in hospitals to monitor a patient""s blood pressure. More particularly, the present invention is an apparatus for use in a fluid pressure monitoring line that allows the system to be pressurized, for calibration, without contaminating the sterile fluid in the system or risking introduction of air into the patient""s fluid line.
In the health care field it is often important to monitor body fluid pressures, such as blood pressure. Pressure transducers are used to continuously monitor such fluid pressures. The transducer includes a sensor which converts fluid pressure to an electrical signal corresponding to the pressure. The electrical signal is then converted to a visual display of the pressure. When measuring a patient""s blood pressure, the transducer is usually connected to a fluid line coupled to the patient""s circulatory system, such as via a catheter introduced into the body.
When monitoring fluid pressure in this and other fields, it is important to verify the accuracy of the pressure transducer, initially and periodically during operation. For example, the transducer is usually zeroed by opening the transducer to atmospheric pressure. The transducer is then calibrated by applying a known test pressure to the transducer and then comparing the transducer pressure reading with the known pressure. Testing the transducer accuracy can also detect malfunctions in the pressure monitoring system.
The fluid pressure line between the patient and the transducer should remain closed and sterile to prevent risk of patient contamination. However, when a test pressure is applied to the transducer fluid line from an external source, there is a risk of contaminating the fluid line. There is also the serious risk of introducing air into the fluid line, which could potentially result in a patient air embolus. Thus, there are some potentially serious problems which can arise when calibrating blood pressure transducers.
One known method of addressing these and other problems includes the use of a bacteria filter and a drip chamber to reduce the risk of patient contamination or air embolus. Although generally effective at avoiding the problems mentioned above, this method is complicated to set up and still requires careful monitoring.
Another method of calibrating a pressure transducer involves the use of negative pressure applied to the back side of the transducer to simulate positive pressure applied to the patient side of the transducer. Although this method avoids the risks associated with patient contamination or air embolism, it is a complicated procedure which is not as accurate as patient side positive pressure calibration.
Recently, modular pressure transducers have been developed having a reusable part and a disposable part. A flexible dome in the disposable part is configured to fit adjacent a reusable diaphragm. Fluid flows into the disposable part, while no fluid contacts the reusable part. Fluid pressure in the disposable part causes the dome to press against the diaphragm and the pressure sensor of the transducer. If the dome is not properly attached, erroneous pressure reading can result and the zero balance can shift. Therefore, it is important to know whether the dome is properly attached to the transducer before the system is connected to the patient.
It would be an advancement in the art to provide an apparatus and method for calibrating pressure transducers in which the fluid path of the pressure monitoring system is pressurized without a potential of injecting air into the patient or contaminating the sterile fluid in the system.
It would be a further advancement in the art to provide an apparatus and method for calibrating pressure transducers which verifies the operation and calibration of modular pressure transducers and domes.
Such an apparatus and method for calibrating pressure transducers is disclosed and claimed herein.
The present invention is directed to a pressure transducer calibration device for use in calibrating a pressure transducer. The calibration device includes a housing which defines a first and second chamber therein. The first and second chambers are separated by a compliant barrier, such as a balloon or other flexible material. A first and second fluid port are in fluid communication with the first chamber, and a third fluid port is in fluid communication with the second chamber.
In operation, the pressure transducer is connected to a fluid pressure monitoring line having a stopcock to control fluid flow in the pressure monitoring line. The stopcock preferably has three fluid ports. Two of the ports are connected to the pressure monitoring line, and the third port is connected to the transducer calibration device.
A removable cap disposed on the calibration device""s first fluid port permits the first chamber to be filled with fluid, such as sterile saline, and thereafter sealed. The second fluid port is configured to be connected to the stopcock. Selective adjustment of the stopcock places the calibration device in fluid communication with the pressure transducer. The calibration device""s third fluid port is preferably configured to be connected in fluid communication with a pressure generation device capable of producing a known fluid pressure.
In one embodiment, the compliant barrier is a balloon disposed within the housing. The balloon has an interior and exterior surface such that the interior surface is in fluid communication with the pressure generation device. The balloon transfers the known fluid pressure from the second chamber to the first chamber such that the pressures are equalized.
In another embodiment, the compliant barrier is an elastomeric tube providing fluid communication between the first and second fluid ports. The first chamber is defined as the interior of the elastomeric tube. The exterior surface of the elastomeric tube is in fluid communication with the second chamber, which is coupled to a pressure generation device. The known pressure in the second chamber is transferred into the first chamber via the elastomeric tube.
In a currently preferred embodiment, the first fluid port is a female luer fitting, the second fluid port is a male luer fitting, and the third fluid port is a female luer fitting. However, persons having ordinary skill in the art will appreciate that other fluid port configurations can be used to connect the calibration device to the monitoring line and to the pressure generation device.
The present invention also includes a method of calibrating a pressure transducer. In a currently preferred embodiment, the pressure transducer is connected to a patient for the purpose of monitoring blood pressure. In the method, the transducer is isolated from the patient, that is, the blood pressure monitoring line is closed to the patient.
A calibration device is coupled to the blood pressure monitoring line in fluid communication with the transducer. As described above, the calibration device includes a housing having two chambers therein. The chambers are separated by a compliant barrier. A known fluid pressure is applied to one chamber and transferred to the other chamber through the compliant barrier and ultimately to the pressure transducer. The pressure measured by the pressure transducer is then calibrated based upon the known fluid pressure within the chambers of the calibration device.
In a currently preferred embodiment of the method, the pressure transducer has a fluid pressure monitoring line and a stopcock in fluid communication with the pressure monitoring line. The fluid pressure monitoring line provides fluid communication between the transducer and a patient. The stopcock has three fluid ports. Two of the ports are connected to the pressure monitoring line and the other port is connected to the transducer calibration device. The stopcock is adjusted to provide fluid communication between the transducer calibration device and the pressure transducer. The first chamber of the calibration device is filled with fluid and capped. A known fluid pressure is applied to the second chamber, such that fluid pressure within the first and second chambers are equalized due to movement of the compliant barrier. The pressure transducer is then calibrated based upon the known fluid pressure within the first and second chambers.
The transducer calibration device within the scope of the present invention can also be used to zero balance the transducer without opening the system to the atmosphere and possible contamination. The calibration device allows the system to remain closed during a zero balancing procedure, eliminating the risk of contamination or air embolus.
In the method of zero balancing the transducer, the pressure within the second chamber is increased. This is conveniently accomplished by injecting a small amount of air, such as 0.05 cc, into the second chamber so that the pressure in the chamber is above about 100 mm Hg. This step is necessary to eliminate the build-up of pressure in the first chamber. The stopcock is adjusted to provide fluid communication between the transducer calibration device and the pressure transducer. Thus, the monitored pressure source is isolated from the transducer and the transducer calibration device. The pressure within the second chamber is released to atmospheric pressure. This causes the pressure within the first chamber to drop to atmospheric pressure through the compliant barrier. The pressure transducer is then zero balanced. The pressure transducer can also be calibrated at this time according to the method described above.